1. Technical Field
The present disclosure relates to vehicle power transmission units, and, more particularly, to wheel-mounted gear reduction units.
2. Description of the Related Art
Wheel drives are used to provide gear reduction at or near the point of service, such as at the hub of a driven wheel. Wheel drives may be used for the large driven wheels commonly found on construction equipment and earth moving vehicles, for example, or for auger bits used in drilling post holes in the ground.
Referring to FIG. 1, a known wheel drive 10 includes a planetary gear system functionally interposed between spindle 12 and wheel hub 14. Spindle 12 is designed to affix to a vehicle frame (not shown), while wheel hub 14 is designed to attach to a vehicle wheel via mounting bolts received in bolt holes 16. When so configured, the planetary gear system operates to receive power from the vehicle motor via an input shaft, and to increase torque and decrease rotational speed of the driven wheel with respect to the input shaft.
The planetary system includes primary planetary stage 70 and secondary planetary stage 80. Primary stage 70 includes sun gear 20 and ring gear 38, with planet gears 24 interposed therebetween and carried on planet gear carrier 26 via respective planet gear axles 28. Primary stage 70 receives power at input coupler 18, which transfers input torque to sun gear 20 via disconnect shaft 22. Secondary stage 80 receives its input from primary planet gear carrier 26 of primary stage 70 via secondary sun gear 30, which is rotationally fixed to carrier 26. Secondary stage 80 provides further gear reduction via secondary planet gears 32 carried on secondary planet gear carrier 34 via respective secondary planet gear axles 36.
Ring gear 38 is driven by both primary and secondary planet gears 24, 32, such that the primary and secondary planetary gear stages 70 and 80 cooperate to substantially reduce the speed of ring gear 38 with respect to input coupler 18 and primary sun gear 20. Ring gear 38 is, in turn, fixed to hub 14 by bolts 40, so the reduced speed and concomitant increase in available torque resulting from the gear reduction is made available to the driven wheel.
Wheel drive 10 utilizes a pair of roller bearings 42, 44 to facilitate the rotation of hub 14 over spindle 12. As shown in FIG. 1, bearings 42, 44 are both disposed between spindle 12, and wheel hub 14.
Roller bearings may be heavily loaded components when used in wheel drives such as wheel drive 10. For example, when a wheel is mounted to the wheel hub and the drive unit is placed in service, the bearings must bear the weight of the vehicle and absorb the dynamic, chaotic forces associated with vehicle operation. These dynamic forces may be particularly acute in certain applications, such as in off-road vehicles, earth-moving equipment, construction and demolition vehicles, etc.